Working machine

ABSTRACT

A working machine includes a hydraulic control apparatus. In a straight travel valve of the hydraulic control apparatus, a communication path and a control valve that opens and closes the communication path are provided. During a combined operation of traveling operation and working operation, a working pressure and a traveling pressure are taken in as pilot pressures on either side. During a small traveling operation in which the traveling operation amount is small, the communication path is unconditionally closed. During a large traveling operation in which the traveling operation amount is large, if the working pressure is higher than the traveling pressure, the communication path is open, and if the working pressure is lower than the traveling pressure, the communication path is closed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a working machine such as a hydraulicexcavator having a hydraulic control apparatus.

2. Description of the Related Art

FIG. 6 shows a hydraulic control apparatus of a hydraulic excavator asan example of a working machine.

A straight travel valve 27 is a two-position four-port switching valvehaving a neutral position x, a straight travel position y, pump ports P1and P2, and actuator ports A and B, and is switched and controlled by asecondary pressure of an electromagnetic proportional switching controlvalve 29 based on a command from a controller 28.

Operation signals according to the operation amounts of remote controlvalves 19 to 24 are input into the controller 28. During a singleoperation in which traveling operation and working operation (operationof working actuators 6, 7, 8, and 12) are performed separately, thestraight travel valve 27 is at the neutral position x.

In this case, the discharged oil of a first pump 25 is supplied to afirst group G1 via a path P1-B of the straight travel valve 27, and thedischarged oil of the second pump 26 is directly supplied to a secondgroup G2 (first pressurized oil supply state).

On the other hand, during a combined operation in which travelingoperation and working operation are performed simultaneously, thestraight travel valve 27 is switched from the neutral position x to thestraight travel position y.

In this case, the discharged oil of the first pump 25 is supplied tohydraulic actuators 6, 7, 8, and 12 except for traveling motors 10 and11 via a path P1-A of the straight travel valve 27 and a pressurized oilsupply pipe L, and the discharged oil of the second pump 26 isdistributed to both traveling motors 10 and 11 (second pressurized oilsupply state).

In this second pressurized oil supply state, since both traveling motors10 and 11 are driven by the common second pump 26, if the amounts of theright and left traveling operations are the same, both traveling motors10 and 11 are supplied with the same amount of oil and rotate at thesame speed. That is to say, straight travel is ensured.

In this case, since the amount of pressurized oil supplied to bothtraveling motors 10 and 11 is decreased by half compared with the firstpressurized oil supply state, the speed is also decreased by half(sudden deceleration) and shock occurs.

As means for reducing the magnitude of this shock, a communication path31 is provided in the straight travel valve 27. During the secondpressurized oil supply state, the pump lines of both pumps 25 and 26communicate with each other via the communication path 31, and part ofthe discharged oil of the first pump 25 is sent to the traveling side(see Japanese Unexamined Patent Application Publication No. 2000-17693).

However, the above-described configuration in which the communicationpath 31 is always open cannot meet the requirements of the following twocases.

(i) The case where working operation is performed during low-speedtraveling (so-called “half-lever traveling” in which the operationamounts of the traveling remote control valves 19 and 22 are small)

If the actuating pressure of the working actuators 6, 7, 8, and 12(working pressure) is higher than the pressure of the traveling motors10 and 11 (traveling pressure), the discharged oil of the first pump 25(the oil of the working side) flows into the traveling side, and thespeed is increased despite the intention of the operator.

If the working pressure is lower than the traveling pressure, thedischarged oil of the second pump 26 (the oil of the traveling side)flows into the working side, and traveling is further decelerated oreven stopped.

Therefore, in such a situation, it is preferable that the communicationpath 31 be closed.

(ii) The case where working operation is performed during high-speedtraveling (so-called “full-lever traveling” in which the operationamounts of the traveling remote control valves 19 and 22 are large)

In a situation where the working pressure is higher than the travelingpressure, part of the oil of the working side is supplied to thetraveling side as intended, and therefore, sudden deceleration can beprevented. However, in a situation where the working pressure is lowerthan the traveling pressure, the oil of the traveling side flows intothe working side, and the speed is decreased more sharply.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide aworking machine having a hydraulic control apparatus that canappropriately control (open or close) a communication path depending onthe situation.

A working machine according to the present invention has the followingbasic configuration.

That is to say, a working machine includes a lower traveling body, anupper rotating body mounted on the lower traveling body, a workingattachment attached to the upper rotating body, and hydraulic actuatorsincluding working actuators that actuate the working attachment, andright and left traveling motors. The hydraulic actuators is separatedinto a first group including one of the right and left traveling motorsand a second group including the other traveling motor. The workingmachine further includes first and second pumps serving as hydraulicpressure sources, and a straight travel valve that switches the flowlines of discharged oils from the pumps. The straight travel valve is ata neutral position to supply the first and second groups with dischargedoils of separate pumps during a single operation in which travelingoperation and working operation are performed separately. In addition,the straight travel valve is switched to a straight travel position andsupplies both traveling motors and the working actuators with dischargedoils of separate pumps during a combined operation in which travelingoperation and working operation are performed simultaneously. Moreover,the straight travel valve enables pump lines of both of the pumps tocommunicate with each other via a communication path in the process ofswitching of the straight travel valve from the neutral position to thestraight travel position. The working machine further includes a controlvalve that opens and closes the communication path. During the combinedoperation, the control valve controls the communication path accordingto the position of the straight travel valve, a working pressure that isan actuating pressure of the working actuators, and a traveling pressurethat is an actuating pressure of the traveling motors, in the followingmanners:

(I) during a small traveling operation in which the traveling operationamount is smaller than a predetermined value, the communication path isunconditionally closed; and

(II) during a large traveling operation in which the traveling operationamount is larger than the predetermined value, if the working pressureis higher than the traveling pressure, the communication path is open,and if the working pressure is lower than the traveling pressure, thecommunication path is closed.

According to the present invention, a working machine is provided with acontrol valve that opens and closes a communication path. During a smalltraveling operation in which the traveling operation amount is smallerthan a predetermined value (half-lever traveling=low-speed traveling),the control valve unconditionally closes the communication path. Duringa large traveling operation in which the traveling operation amount islarger than the predetermined value (full-lever traveling=high-speedtraveling), if the working pressure is higher than the travelingpressure, the control valve opens the communication path, and if theworking pressure is lower than the traveling pressure, the control valvecloses the communication path. Therefore, the following advantages canbe obtained:

(1) The following adverse effects do not occur. During the half-levertraveling, the oil of the working side flows into the traveling side,and the speed is thereby increased, or the oil of the traveling sideflows into the working side, and traveling is thereby furtherdecelerated or even stopped.

(2) During the full-lever traveling, in a situation where the workingpressure is higher than the traveling pressure, the oil of the workingside is supplied to the traveling side as intended, and therefore,sudden deceleration can be prevented. On the other hand, in a situationwhere the working pressure is lower than the traveling pressure, sincecommunication of oil between the traveling side and the working side isblocked, an adverse effect such that the speed is decreased more sharplycan be prevented.

Thus, the communication path can be appropriately controlled (opened orclosed) depending on the situation, and the operability of the combinedoperation can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the overall structure of a hydraulic control apparatusaccording to an embodiment of the present invention;

FIGS. 2A to 2D show the switching of the straight travel valve in theapparatus, using hydraulic symbols;

FIGS. 3A to 3D are half cross-sectional views showing the structure andthe switching of the valve;

FIG. 4 is a half cross-sectional view showing the structure of astraight travel valve according to another embodiment of the presentinvention;

FIG. 5 is a schematic side view of a hydraulic excavator; and

FIG. 6 shows the overall structure of a hydraulic control apparatus ofthe related art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will now be describedwith reference to the drawings.

As an example of a working machine to which the present invention isapplied, a hydraulic excavator will be described. As shown in FIG. 5, ahydraulic excavator includes a crawler-type lower traveling body 1, anupper rotating body 2 mounted on the lower traveling body 1 androtatable around a vertical axis, and a working (excavating) attachment9 attached to the upper rotating body 2. The working (excavating)attachment 9 includes a boom 3, an arm 4, a bucket 5, a cylinder 6 forraising and lowering the boom 3, a cylinder 7 for actuating the arm 4,and a cylinder 8 for actuating the bucket 5.

The hydraulic excavator further includes left and right traveling motors10 and 11 that cause the lower traveling body 1 to travel and a rotatingmotor 12 that causes the upper rotating body 2 to rotate.

FIG. 1 shows the overall structure of a hydraulic control apparatus.

The hydraulic actuators are separated into two groups: a first group G1including the right traveling motor 11, the bucket cylinder 8, and theboom cylinder 6; and a second group G2 including the left travelingmotor 10, the rotating motor 12, and the arm cylinder 7.

The hydraulic actuators of the group G1 are connected in tandem by acenter bypass line C1 with the traveling motor 11 most upstream. Thehydraulic actuators of the group G2 are connected in tandem by a centerbypass line C2 with the traveling motor 10 most upstream. On the otherhand, the hydraulic actuators except for the traveling motors (workingactuators) 6, 7, 8, and 12 are connected in parallel to a pressurizedoil supply line L provided separately from the center bypass lines C1and C2. Reference character T denotes a tank.

In addition, each hydraulic actuator is provided with a hydraulic pilotcontrol valve 13, 14, 15, 16, 17, or 18 that controls its operation, anda remote control valve 19, 20, 21, 22, 23, or 24 that serves asoperating means for switching the hydraulic pilot control valve.

As pressurized oil supply sources for the hydraulic actuators, first andsecond pumps 25 and 26 are provided. The discharged oils of both pumps25 and 26 are supplied to the groups G1 and G2 via a hydraulic pilotstraight travel valve 32.

In the present embodiment, the straight travel valve 32 is afour-position four-port switching valve having four switch positions: aneutral position a at the left end in the figure, a straight travelposition 6 at the right end in the figure, and first and second middlepositions β and γ, and four ports: two pump ports P1 and P2, and twoactuator ports A and B. This straight travel valve 32 is switched andcontrolled by a secondary pressure of an electromagnetic proportionalswitching control valve 29 in response to a command from a controller 33based on operation signals (for example, signals from pressure sensorsthat detect the remote control valve pilot pressures).

That is to say, the straight travel valve 32 is set to the neutralposition α during the single operation of traveling or working. Thisstate is called “first pressurized oil supply state.”

In this first pressurized oil supply state, as in the neutral position xof the straight travel valve 27 in FIG. 6, the discharged oil of thefirst pump 25 is supplied to the first group G1 via a path P1-B of thestraight travel valve 32, and the discharged oil of the second pump 26is directly supplied to the second group G2.

If an independent travel switch 34 is operated, the straight travelvalve 32 is switched to the straight travel position 6. This state iscalled “second pressurized oil supply state.”

In this second pressurized oil supply state, the discharged oil of thefirst pump 25 is supplied to the working actuators 6, 7, 8, and 12 via apath P1-A of the straight travel valve 32 and a pressurized oil supplyline L, and the discharged oil of the second pump 26 is distributed toboth traveling motors 10 and 11 so as to ensure straight traveling.

In addition, the traveling system is completely separated from theworking system, and an independent traveling state is thereby obtained.Therefore, for example, when the working machine travels, hanging aload, the load can be prevented from swinging.

In this case, if switching from the first pressurized oil supply stateto the second pressurized oil supply state is suddenly performed, theamount of the pressurized oil supplied to both traveling motors 10 and11 sharply decreases, the speed is thereby sharply decreased, and shockoccurs.

As a measure against this problem, the straight travel valve 32 isprovided with a communication path 35 for supplying part of thedischarged oil of the first pump 25 to the traveling side, as in thestraight travel valve 27 of the related art.

However, if the communication path 35 is always open, unfavorablesituations can occur during the half-lever traveling and the full-levertraveling depending on the relationship between the working pressure andthe traveling pressure as described above.

To solve this problem, a control valve 36 for opening and closing thecommunication path 35 is incorporated into the straight travel valve 32.

FIGS. 2A to 2D are enlarged views showing the configurations of thestraight travel valve 32 having the control valve 36 at the positions ato 6, respectively, using hydraulic symbols.

FIGS. 3A to 3D show the specific valve structure (half cross-section) ofthe straight travel valve 32. As shown in the figures, a sub-spool 38 isprovided in a main spool 37 that is a spool of the straight travel valve32. The sub-spool 38 can stroke in the horizontal direction in thefigures.

As shown, the diameter of the middle portion of the sub-spool 38 issmaller than the diameter of the right and left end portions thereof(the right and left end portions in FIGS. 3A to 3D. The words “right”and “left” will hereinafter designate directions in FIGS. 3A to 3D).Between the middle portion of the sub-spool 38 and the inner surface ofthe main spool 37, a communication path 35 is formed. Reference numerals39 and 40 denote communicating ports for causing the communication path35 to communicate with the pump ports P1 and P2.

On the right side of the sub-spool 38, a working side pilot chamber 41is provided. On the left side of the sub-spool 38, a traveling sidepilot chamber 42 is provided. The main spool 37 is provided with workingside pilot ports 43 and 44 and a traveling side pilot port 45. Theworking side pilot ports 43 and 44 introduce the working pressure (thepressure of the first pump 25) into the working side pilot chamber 41.The traveling side pilot port 45 introduces the traveling pressure (thepressure of the second pump 26) into the traveling side pilot chamber42. In FIGS. 3A to 3D, reference character Tp denotes a tank port, andreference character Dr denotes a drain port.

The two working side pilot ports 43 and 44 are provided for the purposeof causing the working side pilot chamber 41 to communicate with thetank port Tp or the drain port Dr in the neutral state of the straighttravel valve shown in FIGS. 2A and 3A and in the half-lever travelingoperation state during the combined operation shown in FIGS. 2B and 3B,and for the purpose of causing the working side pilot chamber 41 tocommunicate with the pump port P1 in the full-lever traveling operationstate shown in FIGS. 2C and 3C.

Reference numeral 46 denotes a spring provided in the traveling sidepilot chamber 42. The sub-spool 38 is pressed by a resultant force ofthe force of the spring 46 and the traveling pressure introduced intothe traveling side pilot chamber 42, rightward in FIGS. 3A to 3D (so asto close the communication path 35), and is pressed by the workingpressure introduced into the working side pilot chamber 41, leftward (soas to open the communication path 35).

Thus, the sub-spool 38, the pilot chambers 41 and 42 on either side, thepilot ports 43 to 45, the spring 46, and so on constitute the controlvalve 36. By means of this control valve 36, the communication path 35is opened or closed depending on the position of the straight travelvalve 32, the working pressure, and the traveling pressure as follows.

When the straight travel valve 32 is at the neutral position α, as shownin FIG. 3A, the working side pilot chamber 41 communicates with the tankport Tp and the drain port Dr, and the traveling side pilot chamber 42communicates with the pump port P2 via the traveling side pilot port 45.

Therefore, the pressure (the traveling pressure) is introduced only intothe traveling side pilot chamber 42. Consequently, the sub-spool 38 ispressed rightward to close the communication path 35 (control valve 36).As a result, communication between the pump ports P1 and P2 is blocked,and the first pressurized oil supply state is caused, that is to say,the discharged oil of the first pump 25 and the discharged oil of thesecond pump 26 are separately supplied to the first group G1 and thesecond group G2, respectively.

If the combined operation is performed from this state, transition ismade to the state of FIG. 3B or FIG. 3C depending on the travelingoperation amount.

First, in a half-lever traveling stage in which the traveling operationamount is small, as shown in FIG. 3B, the working side pilot chamber 41communicates with the drain port Dr, and the traveling side pilotchamber 42 continues communicating with the pump port P2 via thetraveling side pilot port 45. Therefore, the communication path 35remains closed.

That is to say, during the half-lever traveling, the communication path35 is unconditionally closed regardless of the working pressure and thetraveling pressure.

Therefore, the following unfavorable situations can be prevented fromoccurring. When the working pressure is higher than the travelingpressure, the discharged oil of the first pump 25 flows into thetraveling side, and the speed is increased despite the intention of theoperator who wants to travel at low speed. When the traveling pressureis higher than the working pressure, the discharged oil of the secondpump 26 (the oil of the traveling side) flows into the working side, andtraveling is further decelerated or even stopped.

Next, from this half-lever traveling state, if the operator performs thefull-lever traveling operation with the intention of traveling at highspeed, as shown in FIG. 3C, the traveling pressure is introduced intothe traveling side pilot chamber 42. On the other hand, the workingpressure is introduced into the working side pilot chamber 41 via thepump port P1 and the working side pilot port 43. The position of thesub-spool 38 is determined by the pressures of the pilot chambers 41 and42 on either side.

That is to say, if the traveling pressure is higher than the workingpressure, the sub-spool 38 is pressed rightward, and if the travelingpressure is lower than the working pressure, the sub-spool 38 is pressedleftward. Therefore, when the traveling pressure is higher than theworking pressure, the communication path 35 is closed, and when thetraveling pressure is lower than the working pressure, the communicationpath 35 is open.

Since the communication path 35 is open in a situation where thetraveling pressure is lower than the working pressure, part of the oilof the working side is supplied to the traveling side as intended,thereby preventing sudden deceleration of traveling.

On the other hand, since the communication path 35 is closed in asituation where the traveling pressure is higher than the workingpressure, an adverse effect such that the oil of the traveling sideflows into the working side and the speed is thereby decreased moresharply is prevented.

By means of the ON operation (switching to ON) of the independent travelswitch 34 shown in FIG. 1, the straight travel valve 32 is switched tothe straight travel position 6. In this case, as shown in FIG. 3D, flowpaths of the discharged oils of the pumps are switched to P1-A and P2-B,the communication path 35 is blocked, and the above-described straighttraveling state (independent traveling state) is caused.

That is to say, when the straight travel valve 32 is switched to thestraight travel position 6, the communication path 35 is unconditionallyclosed. In this case, at the straight travel position 6, an independenttraveling function such that traveling operation is completelyindependent from working operation can be obtained. Therefore, forexample, when the working machine travels, hanging a load, the load canbe prevented from swinging.

As described above, by opening or closing the communication path 35 withthe control valve 36 depending on the situation (whether the half-levertraveling or the full-lever traveling is selected, and the workingpressure and the traveling pressure during the full-lever traveling),the flow of oil during the combined operation can be made desirable andthe operability of the combined operation can be improved.

In addition, the control valve 36 is incorporated into the straighttravel valve 32, that is to say, the communication path 35 and thesub-spool 38 for opening and closing the communication path 35 areprovided in the main spool 37 that is a spool of the straight travelvalve 32, and the sub-spool 38 is actuated by the working pressure andthe traveling pressure. Therefore, it is not necessary to provide aspace for the control valve, and a control circuit. As a result, it iseasy to mount the control valve 36, and the cost can be reduced.

In the present embodiment, the control valve 36 is a hydraulic pilotvalve, the working pressure is introduced into one of the pilot chambersof the control valve 36, and the traveling pressure is introduced intothe other pilot chamber.

In this configuration, the communication path 35 and the sub-spool 38are provided in the main spool 37 that is a spool of the straight travelvalve 32, the pilot chambers are formed on either side of the sub-spool38, the working side pilot ports that introduce the working pressureinto one of the pilot chambers and the traveling side pilot port thatintroduces the traveling pressure into the other pilot chamber areprovided in the main spool 37, and the communication path 35, thesub-spool 38, the pilot chambers, the working side pilot ports, and thetraveling side pilot port constitute the control valve 36.

According to this configuration, the control valve 36 is a hydraulicpilot valve, the working pressure is introduced into one of the pilotchambers of the control valve 36, and the traveling pressure isintroduced into the other pilot chamber. Therefore, opening or closingof the control valve during the full-lever traveling can be performedautomatically and accurately depending on the working pressure and thetraveling pressure.

As a method to realize this configuration, it is possible to take thecommunication path 35 out of the straight travel valve 32, to provide acontrol valve, and to cause the control valve to operate outside asdescribed above.

However, this external control valve method has the following problems.For example, the cost is substantially increased because it is necessaryto newly install a control valve outside in addition to the providing ofa control circuit therefor. Moreover, it is necessary to create a spacefor the control valve in a limited space.

According to the present embodiment, the communication path 35 and thesub-spool 38 are provided in the main spool 37 that is a spool of thestraight travel valve 32, and the working pressure and the travelingpressure are introduced into the pilot chambers on either side of thesub-spool 38, that is to say, the control valve 36 is incorporated intothe straight travel valve 32. Therefore, it is not necessary to providea space for the control valve, and a control circuit. As a result, it iseasy to mount the control valve, and the cost can be reduced. AnotherEmbodiment As shown in FIG. 4, the pilot ports 43 and 45 that cause thepilot chambers 41 and 42, respectively, to communicate with the pumpports P1 and P2, respectively, in the full-lever traveling state duringthe combined operation, may be provided with a throttle. In addition,pilot ports 47 and 48 having a throttle and communicating with the tankport Tp may be added to the working side and the traveling side,respectively.

In both the working side and the traveling side, the pressures generatedin the pilot chambers 41 and 42 can be variously set by the sizes of thethrottles of the two pilot ports 43 and 47 and the sizes of thethrottles of the two pilot ports 45 and 48, respectively. Therefore, thepresent embodiment has the following advantages. For example, freedom ofchoice expands with respect to the size of the spring 46 of thetraveling side. In addition, the pilot pressures on either side can bestabilized.

The above-described double throttle pilot structure may be provided inonly one of the working side and the traveling side.

Although the invention has been described with reference to thepreferred embodiments in the attached figures, it is noted thatequivalents may be employed and substitutions made herein withoutdeparting from the scope of the invention as recited in the claims.

1. A working machine comprising: a lower traveling body; an upperrotating body mounted on the lower traveling body; a working attachmentattached to the upper rotating body; hydraulic actuators includingworking actuators that actuate the working attachment, and right andleft traveling motors, the hydraulic actuators being separated into afirst group including one of the right and left traveling motors and asecond group including the other traveling motor; first and second pumpsserving as hydraulic pressure sources; a straight travel valve adaptedto switch the flow lines of discharged oils from the pumps, the straighttravel valve being at a neutral position to supply the first and secondgroups with discharged oils of separate pumps during a single operationin which traveling operation and working operation are performedseparately, being switched to a straight travel position to supply bothtraveling motors and the working actuators with discharged oils ofseparate pumps during a combined operation in which traveling operationand working operation are performed simultaneously, and enabling pumplines of both of the pumps to communicate with each other via acommunication path in the process of switching of the straight travelvalve from the neutral position to the straight travel position; and acontrol valve adapted to open and close the communication path, wherein,during the combined operation, the control valve controls thecommunication path according to the position of the straight travelvalve, a working pressure that is an actuating pressure of the workingactuators, and a traveling pressure that is an actuating pressure of thetraveling motors, in the following manners: (I) during a small travelingoperation in which the traveling operation amount is smaller than apredetermined value, the communication path is unconditionally closed;and (II) during a large traveling operation in which the travelingoperation amount is larger than the predetermined value, if the workingpressure is higher than the traveling pressure, the communication pathis open, and if the working pressure is lower than the travelingpressure, the communication path is closed.
 2. The working machineaccording to claim 1, wherein, when the straight travel valve isswitched to the straight travel position, the communication path isunconditionally closed.
 3. The working machine according to claim 1,wherein the control valve is a hydraulic pilot valve, the workingpressure is introduced into a first pilot chamber of the control valve,and the traveling pressure is introduced into a second pilot chamber. 4.The working machine according to claim 2, wherein the control valve is ahydraulic pilot valve, the working pressure is introduced into a firstpilot chamber of the control valve, and the traveling pressure isintroduced into a second pilot chamber.
 5. The working machine accordingto claim 3, wherein the communication path and a sub-spool are providedin a main spool that is a spool of the straight travel valve, the firstpilot chamber and the second pilot chamber are formed on either side ofthe sub-spool, a working side pilot port that introduces the workingpressure into the first pilot chamber and a traveling side pilot portthat introduces the traveling pressure into the second pilot chamber areprovided in the main spool, and the communication path, the sub-spool,the first pilot chamber, the second pilot chamber, the working sidepilot port, and the traveling side pilot port constitute the controlvalve.
 6. The working machine according to claim 4, wherein thecommunication path and a sub-spool are provided in a main spool that isa spool of the straight travel valve, the first pilot chamber and thesecond pilot chamber are formed on either side of the sub-spool, aworking side pilot port that introduces the working pressure into thefirst pilot chamber and a traveling side pilot port that introduces thetraveling pressure into the second pilot chamber are provided in themain spool, and the communication path, the sub-spool, the first pilotchamber, the second pilot chamber, the working side pilot port, and thetraveling side pilot port constitute the control valve.